Coiled tubing has been reliably used in land-based hydrocarbon recovery operations for decades, since various well treatment, stimulation, injection, and recovery operations may be more efficiently performed with conveyed coiled tubing than with threadably connected joints of tubulars. A conventional coiled tubing injector may be positioned at the surface of a land-based well or in relatively shallow water of an offshore well, although positioning a conventional tubing injector in a moderate or deep water well is impractical for most offshore coiled tubing operations.
Some injectors have utilized sealed bearings for both land and shallow water operations. Conventional dynamic seals in sealed bearing packages cannot, however, reliably withstand the hydrostatic sea pressure and high operating speeds encountered for a coiled tubing injector working in a deep water environment.
According to one proposal, the subsea tubing injector is protected from the subsea environment by an enclosure, with seals provided between the enclosure and the coiled tubing above and below the injector. An example of this system is discussed in U.S. Pat. No. 4,899,823.
The disadvantages of the prior art are overcome by the present invention, and an improved subsea coiled tubing injector and method of injecting coiled tubing subsea are hereinafter provided.